Bioengineering and the Eye

A special issue of Bioengineering (ISSN 2306-5354).

Deadline for manuscript submissions: closed (31 October 2019) | Viewed by 34011

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Guest Editor
North Texas Eye Research Institute (NTERI), University of North Texas Health Science Center, Fort Worth, TX 76107, USA
Interests: corneal wound healing; cornea trauma; keratoconus; bioengineering; bioprinting; diabetic keratopathy
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Special Issue Information

Dear Colleagues,

Biomedical engineers tackle some extremely difficult challenges, such as rebuilding body parts and organs. On the other hand, biologists tackle difficult challenges of their own, including cell–cell interactions and signaling, cell–matrix communication, and so on. In reality, the two of them—biomedical engineers and biologists—work together to complete their tasks and achieve their goals. In the ocular world, bioengineering is crucial as we move towards the replacement of ocular parts such as the cornea, the retina, the lens, and so on.

Despite significant research, a lot of concepts and technologies remain unexplored. The current SI calls for original research articles, as well as reviews, that tackle ocular problems using bioengineering/biomedical/tissue engineering approaches.

Dr. Dimitrios Karamichos
Guest Editor

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Published Papers (5 papers)

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Research

11 pages, 4560 KiB  
Article
Changes in Epithelial and Stromal Corneal Stiffness Occur with Age and Obesity
by Peiluo Xu, Anne Londregan, Celeste Rich and Vickery Trinkaus-Randall
Bioengineering 2020, 7(1), 14; https://doi.org/10.3390/bioengineering7010014 - 7 Feb 2020
Cited by 10 | Viewed by 5396
Abstract
The cornea is avascular, which makes it an excellent model to study matrix protein expression and tissue stiffness. The corneal epithelium adheres to the basement zone and the underlying stroma is composed of keratocytes and an extensive matrix of collagen and proteoglycans. Our [...] Read more.
The cornea is avascular, which makes it an excellent model to study matrix protein expression and tissue stiffness. The corneal epithelium adheres to the basement zone and the underlying stroma is composed of keratocytes and an extensive matrix of collagen and proteoglycans. Our goal was to examine changes in corneas of 8- and 15-week mice and compare them to 15-week pre-Type 2 diabetic obese mouse. Nanoindentation was performed on corneal epithelium in situ and then the epithelium was abraded, and the procedure repeated on the basement membrane and stroma. Confocal imaging was performed to examine the localization of proteins. Stiffness was found to be age and obesity dependent. Young’s modulus was greater in the epithelium from 15-week mice compared to 8-week mice. At 15 weeks, the epithelium of the control was significantly greater than that of the obese mice. There was a difference in the localization of Crb3 and PKCζ in the apical epithelium and a lack of lamellipodial extensions in the obese mouse. In the pre-Type 2 diabetic obese mouse there was a difference in the stiffness slope and after injury localization of fibronectin was negligible. These indicate that age and environmental changes incurred by diet alter the integrity of the tissue with age rendering it stiffer. The corneas from the pre-Type 2 diabetic obese mice were significantly softer and this may be a result of changes both in proteins on the apical surface indicating a lack of integrity and a decrease in fibronectin. Full article
(This article belongs to the Special Issue Bioengineering and the Eye)
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8 pages, 831 KiB  
Article
Stromal Collagen Arrangement Correlates with Stiffness of the Canine Cornea
by Brian C. Leonard, Krista Cosert, Moritz Winkler, Ariana Marangakis, Sara M. Thomasy, Christopher J. Murphy, James V. Jester and Vijay Krishna Raghunathan
Bioengineering 2020, 7(1), 4; https://doi.org/10.3390/bioengineering7010004 - 25 Dec 2019
Cited by 11 | Viewed by 6599
Abstract
The cornea is the most external layer of the eye and serves two important roles in (1) the refraction of light and (2) protection from the outside environment, both of which are highly dependent on the collagen assembly of the corneal stroma. This [...] Read more.
The cornea is the most external layer of the eye and serves two important roles in (1) the refraction of light and (2) protection from the outside environment, both of which are highly dependent on the collagen assembly of the corneal stroma. This study sought to determine the collagen fiber arrangement of the canine corneal stroma and correlate the stromal organization with tissue stiffness in the anterior and posterior cornea. Collagen organization of the canine cornea was visualized through second-harmonic generation (SHG) imaging, and tissue stiffness of the anterior and posterior corneal stroma was determined by atomic force microscopy. Analysis of the canine anterior corneal stroma using SHG imaging documented intertwining of the collagen fibers with a high degree of fiber branching, with a more lamellar and non-branching posterior stroma. The anterior stroma had significantly higher tissue stiffness in both dogs and humans, when compared with the posterior corneal stroma (canine median: 1.3 kPa vs. 0.3 kPa; human median: 14.6 kPa vs. 2.1 kPa, respectively). There was a direct correlation between corneal collagen stromal organization and tissue stiffness in the dog, which was consistent with other mammalian species previously examined and likely reflects the need for maintenance of rigidity and corneal curvature. Full article
(This article belongs to the Special Issue Bioengineering and the Eye)
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15 pages, 18311 KiB  
Article
Corneal Epithelial–Stromal Fibroblast Constructs to Study Cell–Cell Communication in Vitro
by Tina B. McKay, Dimitrios Karamichos, Audrey E. K. Hutcheon, Xiaoqing Guo and James D. Zieske
Bioengineering 2019, 6(4), 110; https://doi.org/10.3390/bioengineering6040110 - 4 Dec 2019
Cited by 24 | Viewed by 8068
Abstract
Cell–cell communication plays a fundamental role in mediating corneal wound healing following injury or infection. Depending on the severity of the wound, regeneration of the cornea and the propensity for scar development are influenced by the acute resolution of the pro-fibrotic response mediated [...] Read more.
Cell–cell communication plays a fundamental role in mediating corneal wound healing following injury or infection. Depending on the severity of the wound, regeneration of the cornea and the propensity for scar development are influenced by the acute resolution of the pro-fibrotic response mediated by closure of the wound via cellular and tissue contraction. Damage of the corneal epithelium, basement membrane, and anterior stroma following a superficial keratectomy is known to lead to significant provisional matrix deposition, including secretion of fibronectin and thrombospondin-1, as well as development of a corneal scar. In addition, corneal wounding has previously been shown to promote release of extracellular vesicles from the corneal epithelium, which, in addition to soluble factors, may play a role in promoting tissue regeneration. In this study, we report the development and characterization of a co-culture system of human corneal epithelial cells and corneal stromal fibroblasts cultured for 4 weeks to allow extracellular matrix deposition and tissue maturation. The secretion of provisional matrix components, as well as small and large extracellular vesicles, was apparent within the constructs, suggesting cell–cell communication between epithelial and stromal cell populations. Laminin-1β was highly expressed by the corneal epithelial layer with the presence of notable patches of basement membrane identified by transmission electron microscopy. Interestingly, we identified expression of collagen type III, fibronectin, and thrombospondin-1 along the epithelial–stromal interface similar to observations seen in vivo following a keratectomy, as well as expression of the myofibroblast marker, α-smooth muscle actin, within the stroma. Our results suggest that this corneal epithelial–stromal model may be useful in the study of the biochemical phenomena that occur during corneal wound healing. Full article
(This article belongs to the Special Issue Bioengineering and the Eye)
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17 pages, 3708 KiB  
Article
A Hyaluronan Hydrogel Scaffold for Culture of Human Oral Mucosal Epithelial Cells in Limbal Stem-Cell Therapy
by Mazyar Yazdani, Aboulghassem Shahdadfar, Catherine Joan Jackson and Tor Paaske Utheim
Bioengineering 2019, 6(4), 97; https://doi.org/10.3390/bioengineering6040097 - 23 Oct 2019
Cited by 6 | Viewed by 5962
Abstract
Hyaluronan (HA), a major component of the extracellular matrix, plays a key role in cell proliferation, growth, survival, polarization and differentiation. We investigated the optimization of a HA hydrogel scaffold for culture of human oral mucosal epithelial cells (OMECs) for potential application in [...] Read more.
Hyaluronan (HA), a major component of the extracellular matrix, plays a key role in cell proliferation, growth, survival, polarization and differentiation. We investigated the optimization of a HA hydrogel scaffold for culture of human oral mucosal epithelial cells (OMECs) for potential application in limbal stem cell therapy. The effect of the optimized scaffold on OMEC cell sheet morphology, cell metabolic activity and expression of genes associated with stemness, adherence and cell damage was studied. The results indicate that HA hydrogels crosslinked with polyethylene glycol diacrylate (PEGDA) failed to support OMEC attachment and growth. However, HA hydrogel scaffolds dried for three days and coated with 1 mg/mL collagen IV produced a full OMEC sheet. Cell morphology was comparable to control after three weeks culture, maintaining 76% metabolic activity. Of apoptosis-related genes, the pro-apoptotic markers CASP3 and BAX2 were upregulated and downregulated, respectively, compared to control whereas the anti-apoptotic marker BCL2 was downregulated. The expression level of stemness genes ΔNp63α and ABCG2 was significantly higher than control. Genes associated with improved scar-less wound healing (integrin-αV) and protection of the ocular surface (cadherin-1) had ~3-fold increased expression. These data suggest that our optimized HA-hydrogel scaffold could enhance culture of OMEC cell sheets for use in ocular reconstruction. Full article
(This article belongs to the Special Issue Bioengineering and the Eye)
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22 pages, 3237 KiB  
Article
Simulation of the Effect of Material Properties on Soft Contact Lens On-Eye Power
by Joshua Moore, Bernardo T. Lopes, Ashkan Eliasy, Brendan Geraghty, Richard Wu, Lynn White, Ahmed Elsheikh and Ahmed Abass
Bioengineering 2019, 6(4), 94; https://doi.org/10.3390/bioengineering6040094 - 9 Oct 2019
Cited by 8 | Viewed by 7242
Abstract
Purpose: To evaluate the variation in the optical power achieved following soft contact lens eye fitting for spherical and cylindrical lenses with differing hydrogel material properties. Methods: Uniaxial tensile tests were performed on four hydrogel materials 77% water-content (w-c) hydrogel, 74% w-c blue [...] Read more.
Purpose: To evaluate the variation in the optical power achieved following soft contact lens eye fitting for spherical and cylindrical lenses with differing hydrogel material properties. Methods: Uniaxial tensile tests were performed on four hydrogel materials 77% water-content (w-c) hydrogel, 74% w-c blue silicone hydrogel, 74% w-c clear silicone hydrogel, and 64% w-c clear hydrogel (shortly referred to as H77p0, SiH74p5-blue, SiH74p5-clear, and H64p0-clear), under loading conditions that would be expected in vivo. Finite element models of the cornea and contact lens interaction were generated using spherical and cylindrical lenses with powers varying from −10 to +20 D; overall diameters of either 13.5, 14.0, or 14.5 mm; and with material properties matching those determined through experimental testing. Results: The moduli of elasticity for each of the tested hydrogel materials were 0.195 ± 0.027 MPa, 0.277 ± 0.019 MPa, 0.279 ± 0.01 MPa, and 0.457 ± 0.013 MPa for H77p0, SiH74p5-blue, SiH74p5-clear, and H64p0 respectively. The calculated values of effective power change (EPC) showed strong negative correlations with lens power. This was particularly apparent in the higher end of the lens power spectrum (over +5 D), where each of the materials demonstrated a highly linear reduction in EPC with increased lens power. Conclusions: Soft contact lenses composed of a stiffer hydrogel are far more resilient to changes in EPC across the lower end of the lens power spectrum (−10 to +5 D). Beyond this range, the material choice does not have a significant effect on the EPC. Full article
(This article belongs to the Special Issue Bioengineering and the Eye)
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